Double patterning is a technology developed for lithography to enhance feature density in integrated circuits. Typically, the lithography technology is used for forming features of integrated circuits on wafers. The lithography technology involves applying a photo resist, and defining patterns in the photo resist. The patterns in the photo resist are first defined in a lithography mask, and are implemented either by the transparent portions or by the opaque portions of the lithography mask. The patterns in the lithography mask are transferred to the photo resist through an exposure using the lithography mask, followed by the development of the photo resist. The patterns in the patterned photo resist are then transferred to the manufactured features, which are formed on a wafer.
With the increasing down-scaling of integrated circuits, the optical proximity effect posts an increasingly greater problem. When two separate features are too close to each other, the optical proximity effect may cause the features to short to each other. To solve such a problem, double patterning technology is introduced. The closely located features are separated to two masks of a same double-patterning mask set, with both masks used to form features that would have been formed using a single mask. In each of the masks, the distances between the features are increased over the distances between the features in the otherwise single mask, and hence the optical proximity effect is reduced, or substantially eliminated.